Remove destroyed sampler states from the current samplers list
Update current samplers list on shader load

Ideally this should populate the list with matching OBS samplerstate_ts
like the GL code, but unfortunately there is no mapping for that yet
Initialize returned pointer to always trigger NULL checks in callers

Also avoid allocation roundtrip if the file is empty after the BOM
obs-video.c:  Fix minor bug

The pointer here is confusing, so I'm just going to remove it and have
it return the value instead.
Merge branch 'master' of https://github.com/jp9000/obs-studio